Australian Defence Minister David Johnston admitted there was only a slim chance it would be found as debris needs to be positively identified first to nail down a crash site.

"We've got about a week (left), but it depends on the temperature of the water and water depth and pressure as to how long the battery power will last," he told national radio.

Authorities are scouring a massive expanse of ocean for clues and even if the zone is narrowed down, Ocean Shield must tow the equipment at just five kilometres per hour (3.1 mph) for the pinger to be able to pick up a signal.

Malayasia's handling of the crisis has been widely criticised, with Chinese relatives of those on board the missing plane particularly scathing, accusing it of incompetence and even a cover-up. (Malaysia's jet crash announcement draws criticism)

"We would like to confirm that the last conversation in the transcript between the air traffic controller and the cockpit is at 0119 (Malaysian time) and is 'Good night Malaysian three seven zero'," the aviation department said in a statement.

"The authorities are still doing forensic investigation to determine whether those last words from the cockpit were by the pilot or the co-pilot."

Shortly after the final message communications were cut and the Boeing 777, carrying mostly Chinese nationals, vanished from civilian radar.'We are not hiding anything'

The move came after testy exchanges on Monday between foreign journalists and Malaysian Transport and Defence Minister Hishammuddin Hussein, who insisted: "We are not hiding anything, we are just following the procedure that has been set."

Malaysia insists it is being transparent, but has yet to release any details of its investigation into what happened, which has included probing the backgrounds of everyone on the flight, including its crew.

In the early days of their daily press briefings after the plane went missing, Malaysian officials made a series of contradictory statements that added to the confusion.

Notably, there have been about-turns regarding the crucial sequence of events in the plane's cockpit before it veered off course, and Malaysia's armed forces have been criticised for failing to intercept the diverted plane when it appeared on military radar.

While Malaysia remains officially in charge, Australia has assumed increasing responsibility for the search, appointing retired air chief marshal Angus Houston to head a new coordination centre in Perth.

Malaysian Prime Minister Najib Razak is expected in Perth on Wednesday to tour the air base being used a staging post.